/*
  KeePass Password Safe - The Open-Source Password Manager
  Copyright (C) 2003-2021 Dominik Reichl <dominik.reichl@t-online.de>

  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2 of the License, or
  (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

using System;
using System.Diagnostics;

using KeePassLib.Utility;

namespace KeePassLib.Security
{
  /// <summary>
  /// A <c>XorredBuffer</c> object stores data that is encrypted
  /// using a XOR pad.
  /// </summary>
  public sealed class XorredBuffer : IDisposable
  {
    private byte[] m_pbCT;
    private byte[] m_pbXorPad;

    public uint Length
    {
      get
      {
        if (m_pbCT == null) { Debug.Assert(false); throw new ObjectDisposedException(null); }
        return (uint)m_pbCT.Length;
      }
    }

    /// <summary>
    /// Construct a new <c>XorredBuffer</c> object.
    /// The <paramref name="pbCT" /> byte array must have the same
    /// length as the <paramref name="pbXorPad" /> byte array.
    /// The <c>XorredBuffer</c> object takes ownership of the two byte
    /// arrays, i.e. the caller must not use them afterwards.
    /// </summary>
    /// <param name="pbCT">Data with XOR pad applied.</param>
    /// <param name="pbXorPad">XOR pad that can be used to decrypt the
    /// <paramref name="pbCT" /> byte array.</param>
    public XorredBuffer(byte[] pbCT, byte[] pbXorPad)
    {
      if (pbCT == null) { Debug.Assert(false); throw new ArgumentNullException("pbCT"); }
      if (pbXorPad == null) { Debug.Assert(false); throw new ArgumentNullException("pbXorPad"); }
      if (pbCT.Length != pbXorPad.Length)
      {
        Debug.Assert(false);
        throw new ArgumentOutOfRangeException("pbXorPad");
      }

      m_pbCT = pbCT;
      m_pbXorPad = pbXorPad;
    }

#if DEBUG
    ~XorredBuffer()
    {
      Debug.Assert((m_pbCT == null) && (m_pbXorPad == null));
    }
#endif

    public void Dispose()
    {
      if (m_pbCT == null) return;

      MemUtil.ZeroByteArray(m_pbCT);
      m_pbCT = null;

      MemUtil.ZeroByteArray(m_pbXorPad);
      m_pbXorPad = null;
    }

    /// <summary>
    /// Get a copy of the plain-text. The caller is responsible
    /// for clearing the byte array safely after using it.
    /// </summary>
    /// <returns>Plain-text byte array.</returns>
    public byte[] ReadPlainText()
    {
      byte[] pbCT = m_pbCT, pbX = m_pbXorPad;
      if ((pbCT == null) || (pbX == null) || (pbCT.Length != pbX.Length))
      {
        Debug.Assert(false);
        throw new ObjectDisposedException(null);
      }

      byte[] pbPT = new byte[pbCT.Length];

      for (int i = 0; i < pbPT.Length; ++i)
        pbPT[i] = (byte)(pbCT[i] ^ pbX[i]);

      return pbPT;
    }
  }
}
